What Is the Yuasa NP4.5-6 Battery?
The Yuasa NP4.5-6 is a 6V, 4.5Ah Valve Regulated Lead Acid (VRLA) battery built on Absorbed Glass Mat (AGM) technology. It belongs to the well-established Yuasa NP/NPX Series, manufactured in Taiwan by GS Yuasa, the world's second largest lead battery manufacturer.
The product's spec sheet was updated in August 2025 (ver. 1.0), confirming the NP4.5-6 remains an active, current-production item. This is not a legacy or discontinued line.
The battery uses lead calcium grid construction paired with GS Yuasa's proprietary HT X Alloy™ technology. The NP4.5-6 is a safety-critical battery widely specified across UK commercial and public sector installations, from fire alarm panels to emergency lighting systems.
Key Specifications at a Glance
The NP4.5-6 delivers a nominal voltage of 6V with a rated capacity of 4.5Ah (20-hour rate at 20°C).
Physical dimensions are compact: 70mm (L) × 47mm (W) × 101mm (H), with a weight of approximately 0.77kg. This makes it a practical fit for space-constrained alarm panels and distributed backup systems.
The standard terminal type is F1 (Faston .187"), though an F2 (Faston .250") variant is also available. Always confirm which terminal your equipment requires before ordering.
Internal resistance sits at approximately 28mΩ (measured at 1kHz). Maximum discharge currents are rated at 120A for 1 second and 40A for 1 minute, giving the battery strong short-duration surge capability.
Operating temperature ranges are broad: storage and discharge from -20°C to +60°C, and charging from -15°C to +50°C. Self-discharge is approximately 3% per month at 20°C, allowing up to 12 months of storage without permanent capacity loss.
The case is moulded from ABS plastic (UL94:HB standard), with a flame-retardant UL94:V0 variant available for fire-rated installations. Certifications include ISO 9001 (quality management), ISO 14001 (environmental management), EN 18001 (OHSAS health and safety), and UL (Underwriters Laboratories) listing.
Float vs Cyclic Charging: What Every Installer Must Know
The NP4.5-6 supports two distinct charging modes, and using the wrong one is a leading cause of premature battery failure. Getting this right matters more than almost any other operational decision.
Float (standby) charging applies to always-connected applications such as UPS systems, fire alarm panels, and intruder alarm control units. The correct float voltage is 6.825V ±1% per block (2.275V ±1% per cell) at 20°C. The battery sits at full charge, ready to deliver power when the mains supply fails.
Cyclic (boost) charging is used in applications with regular charge and discharge cycles, such as portable equipment or cycled backup systems. The correct cyclic voltage is 7.26V ±3% per block at 20°C.
Temperature compensation is critical, particularly for outdoor or high-temperature UK installations. The float voltage should be corrected by -3mV per cell per °C above 20°C. For a 3-cell, 6V block, that translates to -9mV per degree above 20°C. Ignoring this adjustment in warm enclosures or plant rooms risks overcharging.
Applying cyclic voltage to a float application will shorten the battery's life significantly. This is a common installer mistake, especially when replacing batteries in panels with adjustable charger settings.
The NP4.5-6's HT X Alloy™ technology helps maintain performance at elevated temperatures, reducing the risk of thermal runaway in warm enclosures. Correct charger settings remain the first line of defence.
What Is the NP4.5-6 Used For?
The NP4.5-6 is specified across a wide range of standby and backup power applications:
- Fire and security alarm systems
- UPS backup power
- Emergency lighting
- CCTV systems
- Access control panels
- Auto control systems
- Solar and wind energy support
- Portable power devices
From a UK compliance perspective, BS 5839 (fire detection and alarm systems) and BS EN 50131 (intruder alarm systems) both require periodic battery replacement. This makes the NP4.5-6 a recurring, compliance-driven purchase for facilities managers and security installers, not a one-off buy.
Public sector demand is particularly strong. NHS buildings, schools, and universities face mandatory emergency lighting and fire alarm testing schedules, creating predictable, volume-driven replacement cycles that keep the NP4.5-6 in constant demand.
The battery's compact form factor (70 × 47 × 101mm) suits space-constrained alarm panels and distributed UPS systems where larger cells simply won't fit. With the growth of smart building infrastructure and IoT-connected security systems, compact 6V standby cells like the NP4.5-6 are increasingly specified in modern installations.
The industrial segment is anticipated to hold a 51.12% share of lead acid battery end-use in 2026, driven by rising demand for backup power solutions. The NP4.5-6 sits squarely in this growth segment.
NP4.5-6 vs NP4-6: Which Should You Choose?
The core difference is capacity: the NP4.5-6 offers 4.5Ah versus 4.0Ah for the NP4-6, a 12.5% increase in available energy.
The extra capacity matters most when backup runtime requirements are tight, when devices draw higher currents, or when batteries are installed in warmer environments where effective capacity is reduced by heat.
Both batteries share the same NP/NPX series platform and a similar physical footprint. Always confirm dimensional compatibility before substituting one for the other.
For fire alarm and emergency lighting applications where extended backup duration is required by BS 5839 or a local risk assessment, the NP4.5-6 is the preferred choice. If the original equipment specifies the NP4-6, verify that the charger voltage settings are appropriate for the NP4.5-6 before making the swap.
Compatible Replacement Batteries for the NP4.5-6
The following batteries are confirmed cross-compatible replacements for the Yuasa NP4.5-6:
- MK ES4.5-6
- Enersys Genesis NP4.5-6
- Power Sonic PS-640 F1
Buyers frequently search by OEM part numbers from their original equipment. The NP4.5-6 is a direct drop-in for these models in most applications.
Before substituting any replacement, always verify: voltage (6V), capacity (4.5Ah), terminal type (F1 or F2), and physical dimensions. The Yuasa NP4.5-6 is widely regarded as the reference standard in this battery class; many generic alternatives are specified to match it.
At hardwarexpress, we stock the Yuasa NP4.5-6 with same-day shipping on most orders, next-day UK delivery, and competitive pricing displayed both inc. and ex. VAT. Trade buyers and public sector procurement teams can order the correct replacement quickly and confidently.
Storage, Shelf Life, and Maintenance Best Practices
The NP4.5-6 self-discharges at approximately 3% per month at 20°C. A fully charged battery will lose roughly 36% of its capacity over 12 months at room temperature.
GS Yuasa confirms the battery can be stored for up to 12 months without permanent capacity loss, provided it receives a top-up charge before being put into service. Store batteries in a cool, dry environment; elevated temperatures accelerate self-discharge and shorten shelf life.
Thanks to its oxygen recombination and gas recombination system, the NP4.5-6 is maintenance-free. There is no need to add water or acid at any point during its service life.
If a battery has been in storage for more than 6 months, give it a refresher charge before installation to restore full capacity. This simple step can make the difference between a battery that performs to spec and one that falls short on its first backup cycle.
The NP4.5-6 carries a EUROBAT "Standard Commercial" classification of 3 to 5 years, with Yuasa stating a design life of up to 5 years at 20°C. Achieving the upper end of that range depends on proper storage, correct charging practices, and a stable operating temperature.
Why the Yuasa NP4.5-6 Is Trusted in Safety-Critical Applications
GS Yuasa's position as the world's second largest lead battery manufacturer is not incidental. The NP series is backed by decades of field-proven reliability across fire, security, and emergency power installations worldwide.
The full certification suite matters for procurement teams in regulated sectors: ISO 9001 covers quality management systems, ISO 14001 addresses environmental management, EN 18001 (OHSAS) covers occupational health and safety, and UL listing confirms independent safety testing. Together, these certifications simplify compliance documentation for facilities managers and purchasing departments.
The NP4.5-6 is non-spillable and can be mounted in multiple orientations (except permanently inverted), giving installers flexibility in varied panel configurations. The flame-retardant UL94:V0 case variant is available for fire-rated enclosure requirements.
VRLA AGM technology means zero maintenance and zero water addition throughout the battery's life. For facilities managers overseeing large battery estates across multiple sites, this reduces total cost of ownership considerably.
The broader VRLA market was estimated at approximately £16.4 billion in 2025, with GS Yuasa among the top five global players collectively holding a 35% market share. That scale translates directly into manufacturing consistency, supply reliability, and ongoing product development.
Buying the Yuasa NP4.5-6 in the UK
Before placing an order, confirm these four details: 6V voltage, 4.5Ah capacity, correct terminal type (F1 or F2), and physical fit within your equipment. Getting any one of these wrong means a return and a delay you cannot afford in a safety-critical system.
Always source from authorised channels to ensure a genuine Yuasa product with a valid warranty. Counterfeit and grey-market batteries do circulate, and they carry real risks in fire alarm and emergency lighting applications.
At hardwarexpress, we have been supplying trade and public customers since 2004, giving us over 20 years of experience in this market. We hold deep stock of the NP4.5-6 with same-day shipping on most orders and next-day UK delivery.
Trade accounts, bulk order enquiries, and purchase order support for NHS, schools, and universities are all available. Both inc. VAT and ex. VAT pricing is displayed on every product page, simplifying ordering for VAT-registered trade and business customers.
Final Verdict: Is the Yuasa NP4.5-6 the Right Battery for Your Application?
The NP4.5-6 brings together proven VRLA AGM technology, a compact and versatile form factor, wide application compatibility, strong certification credentials, and a design life of up to 5 years at 20°C. It is the go-to choice for UK fire alarm, emergency lighting, UPS, and access control installations, particularly where compliance with BS 5839 or BS EN 50131 is required.
If there is one operational factor that will determine how long your NP4.5-6 lasts, it is getting the float versus cyclic charging voltage right. Review your charger settings before installation, apply temperature compensation where needed, and the battery will reward you with reliable, full-term service.
Check compatibility with your existing system, confirm your terminal type, and order from a trusted UK supplier with stock available for same-day dispatch. The NP4.5-6 is a battery that earns its reputation every time the mains go down.